1. Technical Field
The present invention relates to a head slider of a hard disk drive, and more particularly, relates to a head slider of tri-pad type for stable flying height over a magnetic disk.
2. Related Art
Generally, a hard disk drive comprises one or more disks being rotated by a built-in spindle motor and one or more magnetic heads for writing and reading data to and from the disks. The actuator rotates about a pivot fixed on the base, and the magnetic heads mounted on one end of the actuator write or retrieve data on and from the target tracks on the disks while moving above the disks by means of the voice coil motor (VCM) provided on the other end of the actuator.
The magnetic heads are each mounted on the respective ends of head gimbals fixed on the actuator arms, and the heads perform data access operations while floating above the surfaces of disks at uniform flying height on an air cushion generated by the high speed rotation of disks. Such magnetic heads are classified into the head stack assembly and the head gimbal assembly depending on the assembled state, and the pole for performing the actual read/write operations is mounted on the slider itself.
As for the head slider, there have been many efforts to design a floating type head slider that is capable of maintaining a constant flying height over the magnetic disk and reducing the spacing loss between the head slider and the magnetic disk for high density and high storage capacity recording. Recently, a pseudo contact head recording technology has been developed for hard disk drive application to reduce the spacing loss between the head slider and the magnetic disk. Examples of contemporary head sliders using pseudo contact head recording technology are disclosed in U.S. Pat. No. 4,218,715 for Magnetic Head Slider Assembly issued to Garnier, U.S. Pat. No. 4,333,229 for Method Of Manufacturing Thin Film Magnetic Head/Slider Combination issued to Ellenberger, and U.S. Pat. No. 4,802,042 for Side-Vented Magnetic Head Air Bearing Slider issued to Strom. Generally the storage capacity and density of the hard disk drive are determined by the magnetic head and the disks, and therefore the recording density varies depending on the flying height of the slider head since the slider head is usually employed for the magnetic head. That is, the lower the flying height is, the higher the obtained recording density is obtained. However, the flying height must be higher than the gliding height because the slider head may crash against the disk surface if the flying height of the slider head is excessively low, and if the flying height is reduced as low as possible without crashing, the head is brought almost into contact with the disk surface. The slider head must use a CSS (contact start and stop) method to land on the disk surface during standstill of the disk drive and lift off from the disk surface when the disk drive starts operation.
Another example of the slider head adopting such pseudo contact head recording method is a tri-pad type head slider as disclosed, for example, in U.S. Pat. No. 5,473,485 for Tripad Air Bearing Magnetic Head Slider issued to Leung et al. A typical tri-pad type head slider consists of two outer side pads (i.e., rails) and a third pad provided at the trailing edge substantially centrally relative to the outer side pads with air bearing surfaces (ABS) for intermittently contacting the disk surface. The CSS (contact start and stop) method adopted by most hard disk drive systems is an important factor for the slider head to land on the disk surface during the standstill of the disk drive and lift off from the disk surface when the disk drive starts operation in order to enhance the reliability of the hard disk drive. Of the three air bearing surfaces, the third and centrally positioned pad performs a recording operation by contacting the disk surfaces by means of the air bearing surface of the middle rail having a head gap and pole. The remaining two air bearing surfaces of side pads keep the overall balance of the head slider. However, as I have observed, the trailing edges of the outer side pads with air bearing surfaces are susceptible to crashes on the disk surface, and adversely affect the cross section of air bearing surfaces as well as the take-off time for lifting off.